Photographic material



Patented Aug. 18, 1942 rno'rocmmc MATERIAL in... David Kendall, Ilford, England, assignoxto Ili'ord Limited, pally Ili'ord, England,- a British com- No Drawing. Application July 30,. 1941,8el-lal This invention relates to photographic ma terials and particularlyfto photographic materials comprising silver halide emulsions containing de-sensitising agents.

The most common use of photographic desensitising agents is in de-sensitising exposed silver halide emulsions, the usual method being to bathe the exposed emulsion in a solution of the de-sensitising agent before development and subsequent processing.

Since the eiiect of the addition of de-sensitising agents is to reduce the light-sensitivity of silver halide emulsions, th addition of de-sensitising agents to photographic silver halide emulsions during the manufacture of such emulsions, i. e. before exposure of the emulsions, is not usual. However, it is known that for some purposes the addition of certain de-sensitising agents to silver halide emulsions prior to exposure is advantageous. Thus, in the case of emulsions designed to record latent images under the influence'of X-rays, the sensitivity of such emulsions to light maybe considerably reduced without serious loss of X-ray sensitivity by the addition of a suitable de-sensitising agent to the emulsion during the manufacture ofthe emulsion. Again, some silver halide emulsions designed for use as positive printing materials tend to become irregularly fogged on development by so-called sulphite fog and it is found that the addition of certain desensitising agents during the manufacture of such emulsions reduces or eliminates this fog.

However, myexperiments have shown that very many of the known de-sensitising agents are unsuitable for one reason or another for incorporation in silver halide emulsions during (tfhe esensltising agents tend to fog the emulsion and. others break down and become inefiective.

manufacture of the emulsions. Thus, some The present invention is based on the discovcry of a specific class of de-sensitising agents which may be incorporated in emulsions for purposes such as those indicated above, without deleterious eflect on the emulsions.

example, the monmmethine cyanine types may According to the present invention; therefore,

photographic materials comprising light-sensitive silver halide emulsions that contain a desensitising agent ar produced byincorporating in silver halide emulsions prior to exposure thereof a de-sensitising agent which is an 'organic compound of the general formula:

wherein X is a sulphur, oxygen or selenium atom, R1 and R2 are alkyl or aralkyl'groups, Y is an;

suitable supportin the usual way.

In Great Britain September 20, '11 Claims. (01.95-4).

acid radical, n is 1, 2, 3 or' 4 and at least one of the benzene rings contains a nuclear-substituted nitro group. l

:Preferably, the de-sensitising agents are compounds of the above generaliormula in which both the atoms X are sulphur atoms and it is also preferred that both benzene nuclei shall contain a. nuclear-substituted nitro group. The l nitro group or groups may be substitutedin any freeposition in the benzene rings, but the 5 and 5 positions are preferred. The groups R1 and R2 are preferably alkyl groups containing up to 4 carbon atoms, e. g. methyl, ethyl, propyl and butyl, but may be higher alkyl groups and, n is preferably 1 or 2.

Specific examples of suitable de-sensitising agents according to the present invention are: 2 :2 -diethyl-5 5' -dinitro-thlacarbocyanine-p-toluene sulphonate, 2 2'-dimethyl-5 5'-dinitro'-thiacarbocyanine-p-tcluene sulphonate and 2:2'-dimethyl-5 5'-dinitro-thiacyanine-p-toluene sulphonate.

The de-sensitising agents of the present invention may be made by any of the known general methods of making cyanine dyes. Thus, for

be prepared by condensing a nitro-substltuted l-methyl-benzthiazole (or oxazcle or selenazole) I quaternary salt with a l-methylthio-benzthiazole (or oxazole or selenazole) which 'may or may not be nitro-substituted Symmetrical dyes of the carbocyanine type may he prepared, for example. by condensing the quaternary salt of a nitrosubstituted l-lnethyl benzthlazole (or oxazole or selenazole) with an alkyl ortho ester, e. g. ethyl ortho iormate'in pyridine solution. Unsymmetrical dyes of the carhocyanine type may be prepared, for example, byv condensing a nitro-substituted l-methyl henzthiazole (or oxazole or selenazole) quaternary salt with a l-acetanilidovinyl derivative of benathiazole (or oxazole or .selenazole) which may or may not he nitrc-substituted.

tion:

' Exmrtn I A gelatin silver iodobromide fast negative.

emulsion containing the equivalent of 300 grams of silver nitrate per gallon of emulsion and suit able for X-ray photography. was prepared and to this was added 31 cos. of 810.01% solution in ethyl alcohol of 2:2'-diethyl 5:5-dinitrothiacarbocyanine-p-toluen'e sulphonate per gallon of emulsion. The emulsion was then-coated ona The addition of the stated de-sensitising agent caused a reduction in the speed of the emulsion to light rays to less than one-eighth of the speed.-

to light rays of the same emulsion-not contain- The following examples illustrate the invenand approximately 40% relative humidity for ten ing the de-sensitising agent, but the speed of the emulsion to X-rays was substantially unaffected by the addition of the stated de-sensitising agent.

In consequence the unexposed emulsion could be handled iii-brighter lighting conditions than would otherwise be necessary, without fear of fogging the emulsion. In addition the emulsion obtained was exceptionally fog-free and had excellent keeping qualities.

EXAMPLE II A washed normal silver bromide emulsion of the type employed in development papers as used for enlarging and containing 3.60 grams of silver per 150 cc. of emulsion was prepared and various quantities of a 0.02% solution of 2 :2'-diethyl 5:5'-dinitrothiacarbocyanine-p-toluene sulphoof alkyl and aralkyl groups, Y is an acid radicle, n is a positive integer less than 5 and at least one of-the benzene rings contains a nuclear substituted nitro group.

3. A photographic element which includes a light-sensitive silver halide emulsion containing a de-sensitising agent which is 'a compound of the general formula: 7

nate were added to separate portions of such emulsion. The emulsions were then coated on paper in the usual way. Some test pieces of the paper were developed in a metol-hydroquinone developer immediately (without exposure) and others were subjected to incubation at 115 F.

days and then developed, without exposure, in a metol-hydroquinone developer.

The density of fog appearing on the developed test pieces was measured in a densitometer and the following results were obtained:

where X is an atom selected from the class con- Foa values Not incubated Inc'ubated Emulsion d2 mi;l8.t d4 mitns.t d2 mitns. d2 mins. d4 mins. d2 mins.

e a e a e at e t. at ev t. at ev t. at 63s. 62 1. 83 p. e r. 65%. 80%.

Original emulsion .02 .18 .24 .06 .30 .40 Emulsion containing 5 ccs. of above solution per pound of emulsion- 0 l2 l8 03 16' l8 Emulsion cont l0 ccs. of above solution per-pound oiem ion 0 .05 .12 '.01 .08 .15 Emulsion containing 20 ccs. of above solution per pound of emulsion 0 02 06 0 05 00 where X is an atom selected from the class consisting of sulphur, oxygen and selenium atoms, R1 and R: are selected from the class consisting of alkyl and aralkyl groups, Y is an acid radicle, n is a positive integer less than 5 and at least one of the benzene rings contains a nuclear substituted nitro group.

2. A photographic element which includes a light-sensitive silver halide emulsion containing a de-sensitising agent which is a compound of the general formula:

R1 Y where X is an atom selected from the class consisting of sulphur, oxygen, and seleniinn atoms, R1 and R: are selected from the class consisting sisting of sulphur, oxygen and selenium atoms,

where Xis an atom selected from the class consisting of sulphur, oxygen and selenium atoms, R1 and R2 are selected from the class consisting of alkyl and aralkyl groups, Y is an acid radicle,

n .is a positive integer less than 3 and atleast one of the benzene rings contains a nuclearsubstituted nitro group.

6. A photographic element which includes a light sensitive silver halide emulsion containing a de-sensitising agent which is a compound of the general formula:

' where'Ri and R2 are selected from the-class consisting of alkyl and aralkyl groups. Y lean acid radicle and n is a positive integer less than 5.

7. A photographic element which includes a light sensitive silver halide emulsion containing a de-sensitis'ing agent which is acompound oi the general formula:

N R/ Y I V l,

' where R1 andR-z are selected from the classconsisting oi'alkyl and aralkyl groups, Y .is an acid radicle and n is a. positive integer less than 3.

8. A photographic element which includes a' light sensitive silver halide emulsion containing a de-sensitising agent w ch is a compound of the general formula:

8,293,261 a I a 3 where R1 and R: are 'alkvl groups containing up to four carbon atoms, Y is an acid radicle and n is a positive integer less than 3.

10 '9. A photographic element which includes a "light sensitive silver halide. emulsion containing 2 :2'-dieth'yl -5: 5'- dinitro thiocarbocyanine-ptoluene sulphonate.

10. A photographic element which includes'a 15 light sensitive silver halide emulsion containing 2':2'-dimethyl -5:5'- dinitro-thiocarbocyanine-ptoluene sulphonate.

11. A photographic element whichincludes a light sensitive silver halide emulsion containing 0 2:2'- dimethyl -5:5'-' dinitro-th'iocyanlne-p-toluene sulphonate. 1 JOHN DAVID KENDAIL 

